An apparatus for testing pixels of a flat panel display has a palette for holding a TFT substrate, drive signal source units, and predetermined voltage source units. The palette is grounded. One of the predetermined voltage source units applies a predetermined voltage to a Cs electrode of each of pixels constituting the TFT substrate so that the predetermined voltage is used as a reference voltage of the TFT substrate 11. The drive signal source units supply drive signals to a gate electrode G and a source electrode S respectively in each of the pixels constituting the TFT substrate. The voltages of the drive signals are floated by predetermined voltages given by the corresponding predetermined voltage source units respectively.
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6. A method of testing pixels of a flat panel display, comprising:
holding said flat panel display by a holding member;
applying a first predetermined voltage to either said holding member or an electrode of a storage capacitor contained in each of said pixels in a condition that a reference voltage of said pixel is applied to said electrode of said storage capacitor, so as to reduce a voltage difference between the holding member and the pixel;
irradiating said flat panel display with an electron beam; and
detecting secondary electrons emitted from each of said pixels of said flat panel display irradiated with said electron beam.
1. An apparatus for testing pixels of a flat panel display, comprising:
an electron beam source for irradiating said flat panel display with an electron beam;
a secondary electron detector for detecting secondary electrons emitted from each of said pixels of said flat panel display irradiated with said electron beam;
a holding member for holding said flat panel display; and
a voltage source unit for applying a first predetermined voltage to either said holding member or an electrode of a storage capacitor contained in each pixel in a condition that a reference voltage of said pixel is applied to said electrode of said storage capacitor, so as to reduce a voltage difference between the holding member and the pixel.
11. An apparatus for testing pixels of a flat panel display, comprising:
an electron beam source for irradiating said flat panel display with an electron beam;
a secondary electron detector for detecting secondary electrons emitted from each of said pixels of said flat panel display irradiated with said electron beam;
a holding member for holding said flat panel display;
a voltage source unit for applying a first predetermined voltage to either said holding member or an electrode of a storage capacitor contained in each pixel in a condition that a reference voltage of said pixel is applied to said electrode of said storage capacitor, so as to reduce a voltage difference between the holding member and the pixel; and
a filter which is provided in a trajectory of secondary electrons emitted from said pixel and to which a second predetermined voltage is applied;
wherein said voltage source unit further applies said first predetermined voltage to said filter;
wherein the filter comprises a grid that removes secondary electrons below a predetermined energy indicating noise from being detected by the secondary electron detector, thereby improving pixel voltage waveform contrast and improving detection of pixel defect.
2. The apparatus for testing pixels of a flat panel display according to
3. The apparatus for testing pixels of a flat panel display according to
4. The apparatus for testing pixels of a flat panel display according to
5. The apparatus for testing pixels of a flat panel display according to
a filter which is provided in a trajectory of secondary electrons emitted from said pixel and to which a second predetermined voltage is applied;
wherein said voltage source unit further applies said first predetermined voltage to said filter.
7. The method of testing pixels of a flat panel display according to
8. The method of testing pixels of a flat panel display according to
9. The method of testing pixels of a flat panel display according to
10. The apparatus for testing pixels of a flat panel display according to
12. The method of testing pixels of a flat panel display according to
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1. Field of the Invention
The present invention relates to an apparatus and method for testing pixels of a flat panel display.
2. Description of the Related Art
A flat panel display (FPD) is a display device for displaying electronic information. An example of the flat panel display (FPD) popularly used in the recent years is a liquid crystal display (LCD) using thin film transistors (TFTs). The liquid crystal display using the TFTs is used in a high-performance laptop computer or the like.
The configuration and operation of the liquid crystal display using the TFTs will be described below. As the basic structure, the liquid crystal display using the TFTs has a liquid crystal panel formed in such a manner that liquid crystal is poured between one glass substrate having TFTs and pixel electrodes formed thereon and the other glass substrate having counter electrodes formed thereon.
Each of the pixels 13 contains a pixel electrode 14, a storage capacitor 15, and a TFT 16. The pixel electrode 14 is made of a light-transmissive material. Generally, the pixel electrode 14 is made of ITO (indium tin oxide). The storage capacitor 15 has an electrode (hereinafter referred to as “Cs electrode”) to which a reference voltage of the pixel 13 is applied. The Cs electrode is grounded. That is, the reference voltage of each TFT 16 is set at a ground level. The TFT 16 functions as a switch. The TFT 16 has a gate electrode G supplied with a row selection signal LR for performing switching control, and a source electrode S supplied with a column selection signal LC as a data signal.
When a voltage VG is applied to the gate electrode G of the TFT 16 (i.e., a row selection signal LR is supplied) while a voltage VS is applied to the source electrode S of the TFT 16 (i.e., a column selection signal LC is supplied) at the time of driving of each pixel 13, the TFT 16 is switched on to increase a drain voltage VD. During that time, the storage capacitor 15 is charged to maintain the drain voltage VD until the next refreshing cycle. By repeating this process to all the pixels 13, the molecular arrangement of liquid crystal between the two glass substrates is controlled so that a two-dimensional image is displayed on the liquid crystal display.
For testing the glass substrate having TFTs and pixel electrodes formed thereon (hereinafter referred to as “TFT substrate”), there has been proposed a method for non-contact judgment of each pixel condition on the substrate on the basis of a voltage contrast technique using an electron beam (U.S. Pat. No. 5,982,190). The TFT substrate testing method using the voltage contrast technique has an advantage that this method is more inexpensive than any related-art testing method using a mechanical probing technique and is higher in testing speed than any optical testing method.
In
The principle of the voltage contrast technique based on the amount of detected secondary electrons will be described below.
The amount of secondary electrons 23 emitted from each pixel 13 of the TFT substrate 11 depends on the polarity of the voltage of the pixel 13 of the TFT substrate 11. When, for example, a pixel 13 in the TFT substrate 11 is driven positively, secondary electrons 23 emitted on the basis of irradiation of the pixel 13 with an electron beam 22 are attracted to the pixel 13 because the secondary electrons 23 have negative electric charges. As a result, the amount of the secondary electrons 23 reaching the secondary electron detector 24 is reduced.
On the other hand, when a pixel 13 in the TFT substrate 11 is driven negatively, secondary electrons 23 emitted on the basis of irradiation of the pixel 13 with an electron beam 22 repel the pixel 13 because the secondary electrons 23 have negative electric charges. As a result, the secondary electrons 23 emitted from the pixel 13 reach the secondary electron detector 24 without reduction in the amount of the secondary electrons 23.
In this manner, the voltage signal waveform of the pixel 13 can be measured on the basis of the fact that the amount of the detected secondary electrons 23 emitted from the pixel 13 depends on the polarity of the voltage of the pixel 13.
In such a test, a method of molding a TFT substrate between a palette for holding the TFT substrate and a prober frame for applying a TFT driving voltage has been proposed in U.S. Pat. No. 6,765,203 to solve the problem that damage of the apparatus in a high-vacuum chamber is caused by breaking of the glass substrate in the high-vacuum chamber.
In
The palette 41 has electrodes (not shown) formed on a stage 45 side and brought into contact with a power distribution portion 46 of the stage 45 opposite to the palette 41, a power distribution portion 42 provided on the prober 44 side and brought into contact with electrodes (not shown) of the prober 44, and a flexible circuit 43 to connect the two power distribution portions 46 and 42 to each other.
The prober 44 is shaped so that a glass portion except a panel 12-formed region of the TFT substrate 11 opposite to the prober 44 is covered with the prober 44. For example, in
The palette 41 and the prober 44 are tightened to each other by fixing stutts such as bolts. Between the palette 41 and the prober 44 after assembling in this manner, the TFT substrate 11 is inserted and held (
For testing, the TFT substrate 11 held between the palette 41 and the prober 44 is carried into a high-vacuum chamber and sat on the stage 45. In the high-vacuum chamber, an apparatus control unit supplies a driving voltage to the electrodes of the prober 44 through the power distribution portion 46 of the stage 45 and the flexible circuit 43 and power distribution portion 42 of the palette 41 in a testing process. The prober pins of the prober 44 supply drive signals to the pixels 13 of the TFT substrate 11 through the electrodes on the glass substrate. On this occasion, the palette 41 (and the prober 44) is grounded to be electrically insulated in the high-vacuum chamber.
In the testing apparatus configured as described above, even in the case where the glass substrate of the TFT substrate 11 in the high-vacuum chamber is broken, broken pieces of glass is not scattered over the stage and other devices in the chamber because the broken pieces remain on the palette 41. Hence, the broken pieces can be collected smoothly, so that damage of the apparatus caused by scattering of the broken pieces can be minimized. Further, because the glass portion of the TFT substrate 11 is covered with the prober 44, drive signals can be supplied to the respective pixels 13 while the glass portion is prevented from being negatively charged (charged-up) on the basis of the electron beam 22.
In the testing apparatus configured as described above, there is however a voltage difference between the prober 44 and a pixel 13 driven near the prober 44. Hence, there is a problem that efficiency in detection of secondary electrons emitted from the driven pixel 13 is lowered by the voltage difference. The influence of the voltage difference between the pixel 13 and the prober 44 on the amount of detected secondary electrons will be described below with reference to
In
In a testing process, the Cs electrode of each pixel and the palette 41 (and the prober 44) are grounded and the drive signal source units 51 and 52 supply drive signals to the source electrode S and the gate electrode G respectively in each pixel. Referring back to
When the TFT substrate 11 is driven positively (e.g., the pixel 13 voltage of the TFT substrate 11 is +5 V) as shown in
On the other hand, when the TFT substrate 11 is driven negatively (the pixel 13 voltage of the TFT substrate 11 is −5 V) as shown in
An object of the invention is to provide an apparatus and method for testing pixels of a flat panel display so that the respective pixels in the whole test region can be tested uniformly and accurately independent of the position in the region.
In order to achieve the object, according to the invention, there is provided an apparatus for testing pixels of a flat panel display, comprising: an electron beam source for irradiating the flat panel display with an electron beam; a secondary electron detector for detecting secondary electrons emitted from each of the pixels of the flat panel display irradiated with the electron beam; a holding member for holding the flat panel display; and a voltage source unit for applying a first predetermined voltage to either the holding member or an electrode of a storage capacitor contained in each pixel in a condition that a reference voltage of the pixel is applied to the electrode of the storage capacitor.
Preferably, the holding member has a palette for putting the flat panel display on its upper surface, and a prober for supplying a drive signal to each pixel to drive the TFT to a predetermined voltage.
In the apparatus for testing pixels of a flat panel display, preferably, the voltage source unit applies the first predetermined voltage as a plus value to the electrode of the storage capacitor. Further preferably, the voltage source unit applies the first predetermined voltage as a plus value to a data signal input terminal of a transistor contained in each pixel and to a switching control signal input terminal of the transistor.
In addition, in the apparatus for testing pixels constituting a flat panel display, preferably, the voltage source unit applies the first predetermined voltage as a minus value to the holding member.
According to the testing apparatus configured as described above, the flat panel display is irradiated with an electron beam generated by the electron beam source. Secondary electrons emitted from each of the pixels of the flat panel display by irradiation with the electron beam are detected by the secondary electron detector. In addition, the voltage source unit applies a first predetermined voltage to either the holding member to hold the flat panel display or the electrode of the storage capacitor contained in each pixel in a condition that the reference voltage of the pixel is applied to the electrode of the storage capacitor. Hence, the voltage difference between the holding member and the pixel is reduced, so that secondary electrons emitted from a pixel near the holding member can be prevented from being absorbed to the holding member. Hence, all pixels in the whole test region can be tested uniformly and accurately independent of the position in the test region, that is, pixels both in the vicinity of the holding member and in a center of the flat panel display can be tested uniformly and accurately.
In addition, the apparatus for testing pixels of a flat panel display further comprises: a filter which is provided in a trajectory of secondary electrons emitted from the pixel and to which a second predetermined voltage is applied; wherein the voltage source unit further applies the first predetermined voltage to the filter.
According to the testing apparatus configured as described above, the filter to which the second predetermined voltage is applied is put in a trajectory of secondary electrons emitted from each pixel so that secondary electrons having energy of not higher than a predetermined value cannot be detected by the secondary electron detector. Hence, only secondary electrons having required energy can be detected by the secondary electron detector. Hence, pixel voltage waveform contrast can be made high on the basis of the amount of detected secondary electrons, so that a defect of each pixel can be detected more accurately.
In order to achieve the object, according to the invention, there is provided a method of testing pixels of a flat panel display, comprising: holding the flat panel display by a holding member; applying a first predetermined voltage to either the holding member or an electrode of a storage capacitor contained in each of the pixels in a condition that a reference voltage of the pixel is applied to the electrode of the storage capacitor; irradiating the flat panel display with an electron beam; and detecting secondary electrons emitted from each of the pixels of the flat panel display irradiated with the electron beam.
In the method of testing pixels of a flat panel display, preferably, the predetermined voltage applying step applies the first predetermined voltage as a plus value to the electrode of the storage capacitor. Further preferably, the predetermined voltage applying step applies the first predetermined voltage as a plus value to a data signal input terminal of a transistor contained in each of the pixels and to a switching control signal input terminal of the transistor.
In addition, in the method of testing pixels of a flat panel display, preferably, the predetermined voltage applying step applies the first predetermined voltage as a minus value to the holding member.
According to the testing method as described above, the flat panel display is held by the holding member. A first predetermined voltage is applied to either the holding member or the electrode of the storage capacitor contained in each pixel in a condition that the reference voltage of the pixel is applied to the electrode of the storage capacitor. The flat panel display is irradiated with an electron beam. Secondary electrons emitted from each of the pixels of the flat panel display irradiated with the electron beam are detected. Hence, the voltage difference between the holding member and the pixel is reduced, so that secondary electrons emitted from a pixel near the holding member can be prevented from being absorbed to the holding member. Hence, all pixels in the whole test region can be tested uniformly and accurately independent of the position in the test region, that is, pixels both in the vicinity of the holding member and in a center of the flat panel display can be tested uniformly and accurately.
Embodiments of the invention will be described below in detail with reference to the drawings.
As shown in
In the testing apparatus configured as described above, the palette 41 (and the prober 44) is electrically grounded. The predetermined voltage source unit 1 applies a predetermined voltage Va to a Cs electrode of each pixel on the TFT substrate 11 so that the voltage Va is used as a reference voltage of the TFT substrate 11. In this embodiment, the predetermined voltage Va has a plus value. The predetermined voltage Va is set in accordance with the voltage level of a predetermined voltage VS applied to a source electrode of each pixel on the TFT substrate 11.
The drive signal source units 51 and 52 supply drive signals to a source electrode S and a gate electrode G respectively contained in each pixel on the TFT substrate 11. Incidentally, the voltages of the drive signals are floated by a predetermined voltage Va given by the predetermined voltage source units 2 and 3. The predetermined voltage Va is a voltage equal in level to the predetermined voltage Va applied to the Cs electrode by the predetermined voltage source unit 1.
The influence of the voltage difference between the driven pixel and the prober on the amount of detected secondary electrons will be described below in the testing apparatus configured according to this embodiment.
In a testing process, each pixel is driven positively or negatively in accordance with the drive signals floated by the predetermined voltage Va. The driven pixel is irradiated with an electron beam emitted from an electron beam source as shown in
In the related-art testing apparatus, when each pixel on the TFT substrate 11 is negatively driven (e.g., each pixel is driven by a drive signal so that the predetermined voltage VS of the source electrode S of the pixel becomes −5 V) as shown in
On the other hand, in the testing apparatus according to this embodiment, the voltage of the TFT substrate 11 becomes −5 V+Va V because the predetermined plus voltage Va is applied to the Cs electrode, whereas the voltage of the prober becomes 0 V because the prober 44 is grounded. Hence, the voltage difference between the prober 44 and a pixel near the prober 44 becomes 5 V−Va V (=0 V−(−5 V+Va V)). Assuming now that the predetermined voltage VS of the source electrode S of each pixel is −5 V, then the preferred value of Va is about 5 V. Hence, in the testing apparatus according to this embodiment, the voltage difference between the prober 44 and a pixel near the prober 44 can be set at 0 V (=0 V−(−5 V+5 V)).
In the testing apparatus configured according to the first embodiment, when the voltage difference between the Cs electrode and the prober is set at zero, secondary electrons emitted from a pixel near the prober 44 on the basis of irradiation with an electron beam are not absorbed to the prober 44, so that secondary electrons can be detected sufficiently even in the vicinity of the prober. In this manner, there is little difference between the amount of detected secondary electrons emitted from a pixel near the prober 44 and the amount of detected secondary electrons emitted from a pixel located in the central portion of the TFT substrate 11. In addition, even in the case where a pixel defect is to be detected in a detected image obtained on the basis of the amount of detected secondary electrons, mistaking of a portion near the prober for a defect can be prevented from being caused by attraction of secondary electrons to the prober side, unlike the related art.
In this manner, the influence of the prober 44 on secondary electrons is reduced, so that the degree of freedom in the shape of the prober can be increased compared with the related art. For example, the thickness of the prober 44 can be increased. Hence, a prober high in mechanical strength can be used as the prober 44.
Although this embodiment has shown the case where a predetermined voltage Va is applied to the Cs electrode of each pixel to thereby set the voltage of the prober 44 at a different value from that of the reference voltage of the TFT substrate 11, the invention is not limited thereto. That is, the invention maybe also applied to the case where the Cs electrode is grounded while a predetermined voltage Va is applied to the prober 44. In this case, the predetermined voltage Va takes a minus value.
In this case, when each pixel on the TFT substrate 11 is negatively driven (e.g., each pixel is driven by a drive signal so that the predetermined voltage VS of the source electrode S of the pixel becomes −5 V), the voltage of the TFT substrate 11 becomes −5 V because the Cs electrode is grounded whereas the voltage of the prober becomes −Va V because the predetermined minus voltage Va is applied to the prober 44. Hence, the voltage difference between the prober 44 and a pixel near the prober 44 becomes −Va V+5V (=−Va V−(−5 V)). Assuming now that the predetermined voltage VS of the source electrode S of each pixel is −5 V, then the preferred value of Va is about 5 V. Hence, in the testing apparatus according to this embodiment, the voltage difference between the prober 44 and a pixel near the prober 44 can be set at 0 V (=−Va V+5 V).
An apparatus for testing pixels of a flat panel display according to a second embodiment of the invention will be described below.
As shown in
The first grid 6 is provided to surround a range of detection of secondary electrons 23 by the secondary electron detector 9. The first grid voltage source unit 5 supplies a predetermined voltage to the first grid 6. An electron beam 22 is reflected by the TFT substrate 11 to thereby form high-energy reflected electrons. The high-energy reflected electrons are made incident on a wall surface of a high-vacuum chamber, so that secondary electrons may be emitted from the wall surface. The first grid 6, however, functions as a filter to prevent the secondary electrons from being detected by the secondary electron detector 9. When, for example, the first grid voltage source unit 5 applies a voltage of −50 V to the first grid 6, secondary electrons having energy of not higher than 50 eV from the wall surface of the high-vacuum chamber are removed, so that secondary electrons as noise incident on the secondary electron detector 9 are removed.
The second and third grids 7 and 8 are provided on an trajectory of secondary electrons 23 between the secondary electron detector 9 and the TFT substrate 11.
The third grid voltage source unit 4 applies a predetermined voltage to the third grid 8. The third grid 8 functions as a filter to detect only secondary electrons having required energy. When, for example, the third grid voltage source unit 4 applies a voltage of −5 V to the third grid 8, secondary electrons 23 having energy of lower than 5 eV are removed by the third grid 8, so that only secondary electrons 23 having energy higher than 5 eV are detected by the secondary electron detector 9. The second grid 7 is grounded. The second grid 7 functions as an auxiliary filter through which secondary electrons passed through the third grid 8 can be efficiently detected by the secondary electron detector.
In the testing apparatus according to this embodiment, the voltage of the Cs electrode is floated by a predetermined voltage Va in the same manner as in the first embodiment. Hence, the predetermined voltage source units 1′ to 3′ further apply predetermined voltages Va to the first, second and third grids 6 to 8 respectively.
In the testing apparatus configured as described above, the secondary electron detector 9 detects secondary electrons emitted from the TFT substrate, through the third grid 8 functioning as a filter and the second grid 7 functioning as an auxiliary filter. On this occasion, the amount of secondary electrons detected by the secondary electron detector 9 varies largely in accordance with the positive or negative driving of the TFT substrate because secondary electrons 23 having energy of not higher than 5 eV are removed by the third grid. As a result, pixel voltage waveform contrast based on the amount of secondary electrons becomes so high that a defect of each pixel can be detected more accurately.
The filtering function of the third grid 8 will be described below in detail with reference to
First, when the TFT substrate 11 is not driven (i.e., the voltage of the TFT substrate 11 is 0 V), secondary electrons 23 emitted from the TFT substrate 11 in the testing process have an energy distribution a as shown in
Next, when the TFT substrate 11 is driven to +5 V or −5 V (i.e., the voltage of the TFT substrate 11 is +5 V or −5 V), the energy distribution of the secondary electrons 23 shifts left or right as shown in
When the third grid 8 is grounded in this condition, the secondary electron detector 9 detects secondary electrons having energy represented by the hatched portion B, from the TFT substrate 11 having a voltage of +5 V (energy distribution b). On the other hand, the secondary electron detector 9 detects secondary electrons having energy represented by the hatched portion C, from the TFT substrate 11 having a voltage of −5 V (energy distribution c). Hence, there is a large difference between the amount of detected secondary electrons in the case where the voltage of the TFT substrate 11 is +5 V and the amount of detected secondary electrons in the case where the voltage of the TFT substrate 11 is −5 V. Hence, pixel voltage waveform contrast based on the amount of detected secondary electrons 23 becomes so high that a defect of each pixel can be detected more accurately (voltage contrast effect).
When a voltage of −5 V is further applied to the third grid 8 in the condition that the TFT substrate 11 is driven to +5 V or −5 V, the secondary electron detector 9 detects secondary electrons having energy represented by the hatched portion B′ in
The value of the voltage applied to the third grid 8 is set in accordance with the voltage level of the predetermined voltage VS applied to the source electrode S of each of pixels constituting the TFT substrate 11. When, for example, the predetermined voltage VS applied to the source electrode S is 5 V or −5 V, the preferred value of the voltage applied to the third grid 8 is −5 V.
In the testing apparatus configured according to the second embodiment, the voltage difference between the Cs electrode and the prober is made small. Hence, secondary electrons emitted from a pixel near the prober 44 by irradiation with an electron beam are hardly absorbed to the prober 44, so that secondary electrons can be detected sufficiently even in the vicinity of the prober. Hence, there is little difference between the amount of detected secondary electrons emitted from a pixel near the prober 44 and the amount of detected secondary electrons emitted from a pixel located in the central portion of the TFT substrate 11.
In addition, secondary electrons having energy of not higher than a predetermined value are removed by grids to which predetermined voltages are applied respectively, so that only secondary electrons having required energy are detected by the secondary electron detector. Hence, pixel voltage waveform contrast can be made high on the basis of the amount of detected secondary electrons, so that a defect of each pixel can be detected more accurately.
Baker, David, Toro-Lira, Guillermo
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